1. Related Application
This application is related to U.S. patent application Ser. No. 687,117, now abandoned, filed even date herewith entitled "METHOD FOR REGENERATIVE HEATING OF DIESEL FUEL" which is incorporated herein by reference.
2. Field of the Invention
This invention relates to the filtering and regenerative heating of diesel fuel as it passes from a fuel tank (or other fuel source) to a diesel engine.
3. Introduction to the Invention
If diesel fuel becomes too cold, higher molecular weight hydrocarbons therein can solidify, causing "clouding" of the fuel. These solids can block the pores of a fuel filter through which the fuel is pumped, causing the engine to lose power (or stop) or preventing the engine from starting. In order to prevent this, various methods have been proposed for heating diesel fuel before it reaches the filter. For disclosure of such methods, reference may be made, for example, to U.S. Pat. Nos. 2,669,299, 3,564,199, 3,935,901, 3,989,019, 4,091,265, 4,372,279, 4,398,084 and 4,406,785 and copending and commonly-assigned U.S. patent application Ser. Nos. 382,259, (now abandoned) 423,589 and 474,390 (now U.S. Pat. No. 4,529,866).
The known systems for the electrical heating of diesel fuel suffer from the disadvantage that the output of the heater must be sufficient to heat all the diesel fuel passing through the fuel system from its storage temperature to a temperature above its cloud point. This is a particularly serious disadvantage when the heater is powered by the electrical system of a vehicle, which has only a limited amount of total power available. Typically, a heater having a power output of 100-150 watts is needed for a car or light truck, with proportionately larger power outputs needed for fuel systems handling larger fuel throughputs, e.g., 450-600 watts for a large truck. Equally important is the fact that the heater may continue to draw power at this rate for a considerable time, so that even if the vehicle batteries can provide the necessary power initially, they cannot continue to do so.
We have now realized that the outgoing diesel fuel (i.e., the fuel which has been filtered) need not be maintained above its cloud point after it has been filtered and that is is therefore possible to reduce the thermal output needed from the heater by passing the outgoing heated and filtered fuel in a regenerative heat-exchange relationship with the incoming fuel to preheat the incoming fuel. This creates a type of regenerative cycle in which low-grade heat that is not necessary after filtering and that would be lost is used to improve thermal efficiency. The present invention makes possible substantial reductions in the power output required of the heater under steady-state conditions, in order to produce a particular increase in the temperature of the fuel as it is filtered, for example a reduction of the power output to less than 25% of that required without any transfer of heat from the outgoing fuel to the incoming fuel as will be seen in the table disclosed later herein.
It is also known, as taught in U.S. Pat. No. 4,372,260, to further heat the fuel after leaving the filter before it is delivered to the engine. The heat-exchanger taught in this disclosure therefore works the opposite of the instant invention wherein the already-heated fuel leaving the filter is used in a heat-exchange with cold incoming fuel to preheat the fuel in a regenerative cycle to improve thermal efficiency.